Upgrading 3 jaw chuck?

[scbvideoboy]

Hi has anybody replaced their 3 jaw chuck (Eldorado) with a known name brand?

I cannot get a consistent reading for round stock. I talked with JT and tightened up the spindle bearings as I was getting .002 or more defection just by pushing on the chuck.

I bought a piece of 316 SS precision ground round bar 1" (sold as less than .0005 run out) in diameter and still have .002 error with my dial indicator.

Dave

[Ken_Shea]

I would not think .002 horribly unreasonable for non precision chuck, are you sure that it is the Chuck and not perhaps, still play in the spindle bearings.
If this is from pushing on the chuck it likely is not the chuck.

It would be a good idea to also remove the chuck, completely disassemble and look for chips/grit/burrs on the jaws/jaw slide/gearing, inside and on the backing plate in particular.

You can also grind the internal jaws concentric, there is proper technique to this, which I have never done, so be sure and get some experienced direction before attempting this.

Ken

[scbvideoboy]

Thanks Ken. I did tightened the spindle nuts on the inside pulleys and the chuck defection is a lot less now.

How common is it for round bar stock to be out of round?

My latest ordeal with this machine is the fact I can't seem to get a round stock to turn true. I can see wobble. That was before I tighten the spindle bearings.

A new chuck from Shoptask is not that expensive, but I thought maybe someone has upgraded.

I am thinking however the mounting is non standard?

I have taken the chuck off and cleaned the jaws and inside spiral groves but not all the way apart. I could swear one of the jaws is longer.

I will measure the other set tonite and see.

Dave

[DareBee]

I dont understand entirely
If your part is not round after turning, you have a problem with your machine (and it is not the chuck).
Generally .002 is good for a chuck, it is very simple to indicate your part true by tapping (with a hammer) your part on the high side and/or using paper or shim stock under the high points.
If you are looking to do a lot of machining from pre-ground material you should have a collet chuck or at least a "set-true" chuck.

[Mcgyver]

yeah what Ken & Darabee said, a three jaw is a convenience, if what you are turning has to be concentric to the bit that is being held, don't use a three jaw, use a collet or 4 jaw . the error lies in the scroll, which is a complex bit of machining. I don't recommend grinding the jaws, unless you are correcting a wear problem on the jaws, but even then the scroll is likely worn as well so you might fix up some bell-mouthing, but you are not going to make it super accurate. even if you grind the jaws on a new chuck, it still will have measurable run out at diameters other than what you ground at - again, the error is in the scroll. 3 jaw runout as low as .002 is pretty darn good.

[Ken_Shea]

Dave,
You can expect standard bar stock to be out of round, but I have found it not bad out of round on short length of a foot or so.
But then turning them to size is why we turn them, so I can see your frustration.

Is the example piece you mention the 1" bar that is not turning true?

How long a piece?

Even a stout 1" bar, if it sticks out far enough and the end is not center supported, it will flex, if the cutter is dull, off center, too low rpm, all these can introduce additional flex.
Also check to be sure the carriage is not sloppy.

Ken

[scbvideoboy]

Hey thanks for all the responses, I'm sure you guys are busy. My shoptask is basically new, got it in July 2005 uncrated in December 2005, and started fiddleling with it, less than a few hours on the lathe the dreaded motor buzz hit and was poping breakers. R

Read up on a lot of fixes for that and ended up redoing all the wiring with solder eyelets, solder motor wire leads, 12awg wiring, the mill too.

Redid the lathe motor pivot, added the shim for the mill pulley tensioner.

Changed the spindle oil. Did all the gibs and tightend all bolts.

Then found out I needed more tools and also sorts of stuff!

What I started doing was a small 1 5/16 diameter ALum tube and I wanted to bore inside to tight fit 2 bearings. All my tests were way off and it seemed I could never get 2 the same.

So I put that aside to work on a 3" length alum solid round stock 2-1/2 diameter for turning. That's when I saw wobble, and even after I turned some off, I did had major runout.

So then I have been fiddling with the spindle and chuck. I bought the 316 SS ground round 1" bar, sold as true to .0005 cut it to 6" inserted in the chuck and was getting the .002 runout AFTER I did all the above tweaks.

I think I have messed up the jaws by grinding and will look for a repair or new chuck. I plan on ordering a 4 jaw also as I will need that.

Is it common to put shims when working with alum? Also do you guys make a sleeve insert for tubing so the jaws don't deform the tube? Or is that a job for a mandrel ( set on order)

Dave

[Ken_Shea]

Dave,
I thought this was supposed to be fun

We all have had our problems, that never stops and is how we learn.

Shimming should not be necessary, although it can be done to purposely off set a cut.

Lathe chucks have a master jaw, usually a mark of some sort next to the screw identifying this, I always snug this one first, then snug the others around the chuck with a final tightening of the master.
Does this make a difference?, I do not know, but it was how I was taught and it does keep our methods consistent which is usually a good thing.

I also always wipe the clamping surface of each jaw with my thumb to be sure nothing is on the face of the jaw to offset the material. As you can imagine it would take very little to cock the piece substantially 6" out from the chuck.

Make sure no burrs are on the shaft end as well.

It is also good practice to not just slap the material in the chuck and tighten away, but hand position it as you snug up the master jaw.

6" sticking out is far enough to introduce some flex and to be supported with a center would be a good idea, when you can.


You likely already know the above but perhaps other readers may not, like Darebee and McGyver
Just kidding guys, I read all your post and you are way ahead of me in machining experience.

Ken

[scbvideoboy]

What I forgot to mention was after all the tweaks and adjustments I put my dial indicator on the outside of the chuck and rotated that by hand using the pulley and that was right at .001 or less for the outside surface so that led me to beleive the jaws were off.

I was taught to tighten all the jaws also.

The ss piece I was testing was 6" long but was inserted into the spindle hole so only about 2 inches were extended.

I knew when I got this there was going to be a steep learning curve but you get to know the machine inside and out.

I just want to make a part!

Dave

[scbvideoboy]

Just an update, I ordered a 4 jaw and live center set from shoptask and made a decision and bought a precision 3 jaw chuck from Bison. Now I'll see about the adaptor for the spindle.

DH

[ZipSnipe]

Dave keep us posted on the precision of the Bison chuck. I,m lookin at getting one those also. I have like .010 run out on my current chuck and I use shims made from soda cans to get it within .003 but I,ve been making pulleys for my mill and am not happy with the slight .003 out of round.

[scbvideoboy]

Just a note, I have been trying to make an adapter plate, and it's slow going as 1: I have no experience, and 2: I put time into other areas of interests.

My first plate was looking good, until I realized it was too thin and the bolt diameter of the new chuck falls within the 100mm shoulder of the spindle mount.

So I started a second piece and flubbed the inside turn and now that is too loose to fit on the spindle shoulder. I am have a hard time on actually getting a contistent measurement of the work diameter. I have a digital caliper but was told not to use that, for measure inside diameters as there is a special tool?

And now as I was working the spindle keeps stopping, I find out the v belts are torn. Low hours and not been over tightend, And of course the number in the parts manual has no USA reference, I saw on the shoptask web site some USA numbers, and that belt crosses over to a L440 which is double the size I need.

DH